Adapt includes for web_preferences.h, now moved into Blink

This class used to live in //content, but it's now part of
Blink's public API, so update includes and namespaces.

Chromium change:

https://chromium.googlesource.com/chromium/src/+/1ac4ca780f9adf3549298115b246695da73af8fc

commit 1ac4ca780f9adf3549298115b246695da73af8fc
Author: Gyuyoung Kim <gyuyoung@igalia.com>
Date:   Fri Sep 11 03:32:51 2020 +0000

    Move content::WebPreferences struct to Blink

    As the first step to convert ViewMsg_UpdateWebPreferences,
    we need to move WebPreferences from //content to
    //third_party/blink because the IPC message passes WebPreferences
    struct.

    So, this CL moves WebPreferences to
    //third_party/blink/public/common/web_preferences as
    a pre-work.

    Additionally, this CL wraps all enums and WebPreferences
    with web_pref namespace to avoid duplicating the existing
    enum types in bliink.

    AX-Relnotes: N/A

    Bug: 1097943

app/brave_main_delegate_browsertest.cc

@@ -19,7 +19,7 @@
 #include "components/safe_browsing/core/features.h"
 #include "content/public/browser/render_view_host.h"
 #include "content/public/common/content_features.h"
-#include "content/public/common/web_preferences.h"
+#include "third_party/blink/public/common/web_preferences/web_preferences.h"
 #include "content/public/test/browser_test.h"
 #include "gpu/config/gpu_finch_features.h"
 #include "net/base/features.h"
@@ -46,7 +46,7 @@ IN_PROC_BROWSER_TEST_F(BraveMainDelegateBrowserTest, DisableHyperlinkAuditing) {
       base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kNoPings));
   content::WebContents* contents =
       browser()->tab_strip_model()->GetActiveWebContents();
-  const content::WebPreferences prefs =
+  const blink::web_pref::WebPreferences prefs =
       contents->GetOrCreateWebPreferences();
   EXPECT_FALSE(prefs.hyperlink_auditing_enabled);
 }